Phase array systems have become commonplace, having several uses. The most common use for phased array systems is radar systems (i.e., pulse radar and Doppler shift radars). As a matter of fact, phased array radar has replaced most of the previous generations of mechanical sweep radar systems because there is a lower likelihood of failure due to wear since mechanic components are replaced with electronics and because the sweep rates are much higher.
Turning to FIG. 1, block diagram illustrating the basic functionality of a conventional phased array system 100. System 100 generally comprises a signal generator 102, phase shifters 104-1 to 104-K, a phased array 106 that includes radiators 106-1 to 106-K, and a direction controller 108. In operation, the signal generator 102 provides a signal that is to be transmitted (i.e., pulse for a pulse radar). Based on the desired direction, the direction controller 108 provides control signals to the phase shifters 104-1 to 104-K, which varies the phase of the signal provided to each of the radiators 106-1 to 106-k within the phased array. Because the signals transmitted through radiators 106-1 through 106-K are generally out-of-phase with one another, constructive and destructive interference of the radiated signal forms a beam in a desired direction.
These conventional systems, though, have been limited to conventional radio frequency (RF) frequency ranges. For example, the frequency range for conventional radar is between 3 MHz (for HF-band radar) and 110 GHz (for W-band radar). A reason for the use of these relatively low frequency ranges is that there has, historically, been an unavailability of compact semiconductor sources of coherent radiation at the terahertz frequency range (which is generally between 0.1 THz and 10 THz). Generally, electronics and oscillators in the microwave range run out of power gain with increasing frequency, and typical broadband infrared blackbody sources begin losing available power within this region. Use of terahertz radiation, however, is highly desirable because of its unique properties. Namely, terahertz radiation has properties of lower frequency radiation (i.e., microwaves) in that it can be generated electrically and higher frequency radiation (i.e., visible light) in that it can be controlled using optics.
Today, there exists two general types of terahertz sources: incoherent source and coherent sources. The incoherent sources are generally broadband incoherent thermal sources, which includes ultra-short femtosecond pulsed laser exciting photo conductive antennas, nonlinear electro-optical crystals, or non-linear transmission lines that suffers from very poor conversion efficiency (1 W laser pulse produces broadband energy in the nW-mW range). The coherent sources are generally narrowband continuous wave (CW) coherent sources which include diode multiplying microwave oscillators, gas lasers using carbon dioxide laser pumping methanol or cyanic acid, optical down conversion by difference mixing, and semiconductor quantum lasing. These coherent sources, though, generally consume a large amount of power, are not compact, require exotic materials, and/or are expensive.
Therefore, there is a need for a compact source of terahertz radiation, namely integrated into an integrated circuit.
Some examples of conventional circuits are: Williams, “Filling the THz Gap,” doi:10.1088/0034-4885/69/2/R01; Heydari et al., “Low-Power mm-Wave Components up to 104 GHz in 90 nm CMOS,” ISSCC 2007, pp. 200-201, February 2007, San Francisco, Calif.; LaRocca et al., “Millimeter-Wave CMOS Digital Controlled Artificial Dielectric Differential Mode Transmission Lines for Reconfigurable ICs,” IEEE MTT-S IMS, 2008; Scheir et al., “A 52 GHz Phased-Array Receiver Front-End in 90 nm Digital CMOS” JSSC December 2008, pp. 2651-2659; Straayer et al. “A Multi-Path Gated Ring Oscillator TDC With First-Order Noise Shaping,” IEEE J. of Solid State Circuits, Vol. 44, No. 4, April 2009, pp. 1089-1098; Huang, “Injection-Locked Oscillators with High-Order-Division Operation for Microwave/Millimeter-wave Signal Generation,” Dissertation, Oct. 9, 2007; Cohen et al., “A bidirectional TX/RX four element phased-array at 60 HGz with RF-IF conversion block in 90 nm CMOS processes,” 2009 IEEE Radio Freq. Integrated Circuits Symposium, pp. 207-210; Koh et al., “A Millimeter-Wave (40-65 GHz) 16-Element Phased-Array Transmitter in 0.18-μm SiGe BiCMOS Technology,” IEEE J. of Solid State Circuits, Vol. 44, No. 5, May 2009, pp. 1498-1509; York et al., “Injection- and Phase-locking Techniques for Beam Control,” IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 11, November 1998, pp. 1920-1929; Buckwalter et al., “An Integrated Subharmonic Coupled-Oscillator Scheme for a 60-GHz Phased Array Transmitter,” IEEE Transactions on Microwave Theory and Techniques, Vol. 54, No. 12, December 2006, pp. 4271-4280; and PCT Publ. No. WO2009028718.